This is Ove Persson and Evy Persson at the Ajvide excavations in Gotland, Sweden. Credit: [Photo taken by Goran Burenhult].

An analysis of 5,000-year-old DNA taken from the Stone Age remains of four humans excavated in Sweden is helping researchers understand how agriculture spread throughout Europe long ago. According to Pontus Skoglund from Uppsala University in Sweden and colleagues, the practice of farming appears to have moved with migrants from southern to northern Europe.

Agricultural know-how wasn't the only thing that early European farmers introduced to the region. Based on their genetic data, Skoglund and the researchers say that Europe's first farmers eventually mixed their genes with the hunter-gatherers who lived there-a relationship that set the stage for today's modern European genome.

"We analyzed genetic data from two different cultures-one of hunter-gatherers and one of farmers-that existed around the same time, less than 400 kilometers (249 miles) away from each other," said Skoglund.

"After comparing our data to modern human populations in Europe, we found that the Stone Age hunter-gatherers were outside the genetic variation of modern populations but most similar to Finnish individuals, and that the farmer we analyzed closely matched Mediterranean populations."

These findings likely have something to do with the expansion of farming across Europe, according to the researchers.

"When you put these findings in archaeological context, a picture begins to emerge of Stone Age farmers migrating from south to north across Europe," said Skoglund. "And the result of this migration, 5,000 years later, looks like a mixture of these two groups in the modern population."

The researchers report their data in the journal Science, which is published by AAAS, the nonprofit international science society.

Most experts agree that the agricultural way of life originated about 11,000 years ago in the Near East before it reached the European continent some 5,000 years later. But this new study should help scientists understand the impact of that agricultural revolution on human diversity.

Skoglund and his colleagues performed their analysis with the ancient remains of three hunter-gatherers who were associated with the Pitted Ware Culture and excavated from the island of Gotland, Sweden, along with those of a farmer, who was associated with the Funnel Beaker Culture and excavated from Gokhem parish, Sweden.

"We know that the hunter-gatherer remains were buried in flat-bed grave sites, in stark contrast to the megalithic sites that the farmers built," said Mattias Jakobsson, a senior author of the Science report, also from Uppsala University. "The farmer we analyzed was buried under such a megalith, and that's just one difference that helps distinguish the two cultures."

Ancient hunter-gatherers had a distinct genetic signature that was similar to that of today's northern Europeans, while the farmer's genetic signature closely resembles that of southern Europeans, according to the researchers. Interestingly, these ancient genomes don't share many similarities with modern-day Swedes, despite their discovery and excavations in Sweden.

"The fact that the hunter-gatherers are most similar to Finns, Orcadians and other extreme-northern populations suggests that they were indeed the last major part of the Mesolithic meta-population that populated large parts of Europe before the early farmers appeared," said Anders Gotherstrom of Uppsala University, who is another senior author of the Science report.

"And the fact that the farmer is most similar to southeastern Europeans makes sense too, as that is from where the spread of agriculture north and eastward started."

"The results suggest that agriculture spread across Europe in concert with a migration of people," added Skoglund. "If farming had spread solely as a cultural process, we would not expect to see a farmer in the north with such genetic affinity to southern populations."

The researchers suggest that Europe's early, intrepid farmers traveled north across the continent, settled in the northern regions and eventually mixed with resident hunter-gatherer populations. Consequently, the genomes of most modern Europeans were likely shaped by this prehistoric migration that first brought farming to the continent, they say.

The report by Skoglund et al. was supported by the Lars Hierta Memorial Foundation, Nilsson-Ehle Donationerna, Marie Curie Actions, the Danish National Research Council, the Royal Swedish Academy of Science and the Swedish Research Council.

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